Carrier for uranium oxide pellets

ABSTRACT

A carrier of uranium oxide pellets suitable for use in dewaxing and sintering of said pellets has a molybdenum or stainless steel base on which there are multiple layers of corrugated molybdenum sheets for holding the pellets within the depressions of the parallel corrugations. The molybdenum sheets are placed above each other with the corrugations running in about the same general direction. The separation of these sheets is by the uranium oxide pellets during the sintering operation and by molybdenum cylinders of a larger diameter than the pellets during the dewaxing operation.

States atem [72] lnventors JamesA.Rode

[56] References Cited UNITED STATES PATENTS St. Louis;

Paul W. Hubert, Pevely, both 0t Mo.

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ABSTRACT: A carrier of uranium oxide pellets suitable for use indewaxing and sinterin denum or stainless steel base on which there aremulti layers of corrugated molybdenum sheets for holdin lets within thedepressions of the parallel corru molybdenum sheets are placed aboveeach other with the corrugations running in about the same generaldirection. The separation of these sheets is by the uranium oxide ingthe sintering operation and by molybdenum c larger diameter than thepellets during the dewaxing operation.

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SHEET 2 BF 2 INVENTORS JAMES A. RODE PAUL W. HUBERT BY QM luau,

CARRIER FOR URANIUM OXIDE PELLETS FIELD OF THE INVENTION This inventionrelates to a carrier for uranium oxide pellets in the dewaxing andsintering operations of the process for preparing uranium oxide pelletsfor the nuclear reactor.

SUMMARY OF THE INVENTION The carrier of this invention has a metallicsupport base resistant to the corrosive emironment during the dewaxingand sintering of the uranium oxide pellets. On the support base is afirst molybdenum sheet which is removable therefrom. The sheet hasparallel corrugations thereon with depressions to hold the pellets. Atleast one additional corrugated molybdenum sheet used for holdingadditional pellets is placed above the first sheet which is supported byeither the pellets during the sintering operation or by a plurality ofmolybdenum cylinders of a diameter greater than the pellets during thedewaxing operation. For the sintering operation one or more sheets ofmolybdenum may be advantageously placed above the last layer of pelletsto serve as a heat shield for more even distribution of the heat amongthe pellets to provide a more uniform sintered product.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings illustratethe preferred embodiments of this invention wherein FIG. 1 is aperspective view of a carrier suitable for holding uranium oxide pelletsfor dewaxing and FIG. 2 is a perspective of a carrier suitable forholding the pellets for sintering.

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the production of uraniumoxide pellets, finely ground or preferably micronized uranium dioxidepowder is initially mixed with an organic binder such as polyvinylalcohol and Carbowax. The admixture is then agglomerated and pressedunder a pressure in the range between 30 to 80 t.s.i. to producecylindrical pellets of a sufficiently high green strength to withstandsubsequent treatments and to provide strong and sound finished pellets.The organic binder used for pelletizing must be first removed toeliminate high contamination of the final products by primarily carbonand nitrogen. Generally, the binder is removed by a treatment commonlycalled dewaxing," using a mixture of steam and a small amount ofhydrogen or crack ammonia, the latter being used to prevent oxidation ofU and at a temperature of about 800 C. After the binder is removed, thedewaxed pellets are sintered at a temperature of about 1,650 C. in areducing atmosphere to about 95 percent or more of the theoreticaldensity.

For commercial production of uranium oxide pellets a large amount ofpellets is being handled in a short period of time either automaticallyor semiautomatically. The design of a carrier for handling the pelletsfor dewaxing and sintering becomes an important aspect of a successfulcommercial uranium oxide pelletizing plant. We have discovered thaturanium oxide pellets can be handled efficiently and with minimum manualmanipulation using the carrier of this invention for the dewaxing andsintering operations and more particularly the carrier of this inventionproduces a more uniformly sintered product. Further to illustrate thisinvention two specific embodiments of this invention are describedhereinbelow with reference to the accompanying drawings.

Referring initially to MG. 1 the carrier of this invention which isspecially adapted for dewaxing operations has a supporting base II whichhas a rectilinear flat main body 12 and two railings 13 and 14 on theopposite sides of the base II. The supporting base 11 should beconstructed from a metal which is substantially resistant to corrosionat the ambient environment during dewaxing operations. We foundstainless steel or lnconel eminently suitable for this purpose. Thesupporting base 11 may be molded or extruded into the form shown in FIG.1.

On top of the supporting base II are two rectangular molybdenum sheets15 and I6 placed side by side with their opposite outer edges parallelto and preferably abutting the railings I3 and 14. The molybdenum sheetsare corrugated with substantially parallel depressions 17 extending thewhole length of the sheet. The depressions [7 of the corrugations aredesigned to hold multiple rows of uranium pellets 24 with each rowseparated from its adjacent rows by a fixed distance of about one to twotimes the diameter of the pellets.

Above the first layer of molybdenum sheets 15 and 16 are two similarlycorrugated molybdenum sheets 18 and I9 each separated from itscorresponding adjacent sheet at a vertical. distance greater than thediameter of the pellets by two rows of molybdenum cylinders 20 placed atthe outermost rows of depressions of the corrugated sheets. The use ofmolybdenum cylinders provided a space above the pellets thus allowingthe decomposed vaporous material during dewaxing to escape therefrom.Two or more layers of similar corrugated molybdenum sheets 21 may beprovided for holding additional pellets for dewaxing with each separatedfrom its adjacently above or below sheets with molybdenum cylinders 20.

The corrugated molybdenum sheets may be made by any method. They can bemolded, stamped or pressed, for example, from a flat sheet to thedesired form. The thickness of the corrugated sheet may be varieddepending on the size of the pellets and on the load exerted thereon.Because of the corrugation which has the advantage of strengthening thesheet, a thickness about one-tenth inch has been found adequate forhandling pellets of common sizes.

For sintering, the carrier described above may be used. However, sincemost volatile materials have escaped from the pellets in the dewaxingoperation, the space provided between the corrugated sheets by themolybdenum cylinders may be eliminated. Also, if a stainless steel or anlnconel supporting base were used for the dewaxing operation, it may beadvantageous to change the base to a more temperature resistant materialsuch as molybdenum because sintering of uranium dioxide pellets isconducted at a much higher temperature, i.e., about 1,650 C. We foundthe modification of the carrier can be accomplished simply by pushingeach of the two stacks of uranium oxide pellets on the corrugatedmolybdenum sheets onto a molybdenum supporting base and by removing themolybdenum cylinders from the edge depressions thereof. The resultantcarrier now is in the form substantially as shown in FIG. 2. In thisdrawing, the supporting base 22 made of molybdenum has generally thesame configuration as the supporting base for the dewaxing carrier 10,except it is about half the width. The corrugated sheets 23 now areseparated solely by the dewaxed pellets 24. Dewaxing does not increasethe diameter of the pellets and therefore it will be understood that thepellets 24 in FIG. 2 have about the same diameter as the pellets shownin FIG. I.

To form a heat shield which would allow a more even heat distributionwithin the stack of pellets and hence a more uniform sintered products,one or more layers or corrugated molybdenum sheets 25 may be placedabove the topmost layer of pellets 26. The molybdenum sheets used asheat shields may be separated from each other with molybdenum spacers 27placed about four comers and at the center between the sheets 25.

The carrier of this invention can be utilized in modern automatic orsemiautomatic pelletizing plants for the manufacture of ceramic grade U0fuel elements. In the modern pelletizing plants, U0, pellets arecompacted continuously. These pellets are then placed on the corrugatedsheet either individually or one row at a time. Once the required numberof layers of pellets are filled, the carrier is sent to the dewaxingfurnace for the removal of the binder therein. Subsequent to dewaxing,the stacks of pellets are directly transferred to a new supporting base;thereon the molybdenum spacers are removed and the heat shield is placedthereon. After the modification, the carrier is sent into the sinteringfurnace for the required treatmentv Because the pellets are orderlyarranged in rows, handling the sintered product subsequently is equallysimplified.

We claim:

l. A carrier for uranium oxide pellets suitable for use in the dewaxingand sintering operations of said pellets which comprises:

a. a metallic support resistant to corrosive actions under thetemperatures and ambient conditions of the dewaxing and sinteringoperations;

b. a first corrugated molybdenum sheet positioned on said metallicsupport and being removable therefrom, said molybdenum sheet havingsubstantially parallel corrugations with depressions for holding aplurality of cylindrical uranium pellets prepared for subjection to atleast one of said dewaxing or sintering operations and c. at least oneadditional corrugated molybdenum sheet having substantially parallelcorrugations of the same dimensions as said first sheet for holdingadditional uranium pellets, each of said additional molybdenum sheetsbeing positioned above and removable from a lower molybdenum sheetseparated either by the pellets placed therebetween or by a plurality ofmolybdenum spacers placed between the sheets and the thickness of suchspacers being adapted to be greater than the diameter of the pellets.

2. A carrier for uranium oxide pellets suitable for use in the dewaxingof said pellets which comprises:

a. a metallic support resistant to corrosive actions under thetemperature and ambient conditions of the dewaxing operation;

b. a first corrugated molybdenum sheet removably positioned on saidmetallic support, said sheet having substantially parallel corrugationswith depressions for holding a plurality of cylindrical uranium pelletsprepared for subjection to said dewaxing operation; and

c. at least one additional corrugated molybdenum sheet havingsubstantially parallel corrugations of the same dimensions as those ofsaid first sheet for holding additional uranium pellets, each of saidadditional sheets being positioned above and removable from a lowermolybdenum sheet separated by a plurality of molybdenum spacers placedbetween the sheets, the thickness of such spacers being adapted to begreater than the diameter of said pellets so as to leave spaces abovethe pellets for the escape of vaporous material during the dewaxingoperation.

3. A carrier according to claim 2 wherein the metallic support is madeof stainless steel or molybdenum.

4. A carrier according to claim 2 wherein the molybdenum spacers for thecorrugated sheets are molybdenum cylinders having a diameter adapted tobe greater than the diameter of the pellets and at least some of saidmolybdenum cylinders are positioned on the corrugations adjacent to theedges of the sheets.

5. A carrier according to claim 2 wherein the carrier has at least threesheets of corrugated molybdenum for carrying the pellets for thedewaxing operation.

6. A carrier for uranium oxide pellets according to claim 2 in which thedistance between the corrugations in the molybdenum sheets is adapted tobe from about 1 to about 2 times the diameter of the pellets.

7. A carrier for uranium oxide pellets suitable for use in the sinteringof said pellets which comprises:

a. a metallic support resistant to corrosive action under thetemperature and ambient conditions of the sintering operation;

b. a first corrugated molybdenum sheet positioned on said support andremovable therefrom, said sheet having substantially parallelcorrugations with depressions for holding a plurality of cylindricaluranium pellets prepared for subjection to the sintering operation; and

c. at least one additional corrugated molybdenum sheet havingsubstantially parallel corrugations of the same dimensions as those ofsaid first sheet for holding additional uranium pellets, each of saidadditional sheets being positioned above and removable from a lowermolybdenum sheet separated therefrom by the pellets placed thercbetween.8. A carrier according to claim 7 wherein the metallic support is madeof stainless steel or molybdenum.

9. A carrier according to claim 7 wherein the carrier has at least fivesheets of corrugated molybdenum for carrying the pellets for thesintering operation, and at least one corrugated molybdenum sheet whichdoes not carry pellets and which is spaced above the top sheet thatcarries pellets to form a heat shield and produce an even heatdistribution within the mass of pellets.

10. A carrier for uranium oxide pellets according to claim 7 in whichthe distance between the corrugations in the molybdenum sheets isadapted to be from about i to about 2 times the diameter of the pellets.

2. A carrier for uranium oxide pellets suitable for use in the dewaxingof said pellets which comprises: a. a metallic support resistant tocorrosive actions under the temperature and ambient conditions of thedewaxing operation; b. a first corrugated molybdenum sheet removablypositioned on said metallic support, said sheet having substantiallyparallel corrugations with depressions for holding a plurality ofcylindrical uranium pellets prepared for subjection to said dewaxingoperation; and c. at least one additional corrugated molybdenum sheethaving substantially parallel corrugations of the same dimensions asthose of said first sheet for holding additional uranium pellets, eachof said additional sheets being positioned above and removable from alower molybdenum sheet separated by a plurality of molybdenum spacersplaced between the sheets, the thickness of such spacers being adaptedto be greater than the diameter of said pellets so as to leave spacesabove the pellets for the escape of vaporous material during thedewaxing operation.
 3. A carrier according to claim 2 wherein themetallic support is made of stainless steel or molybdenum.
 4. A carrieraccording to claim 2 wherein the molybdenum spacers for the corrugatedsheets are molybdenum cylinders having a diameter adapted to be greaterthan the diameter of the pellets and at least some of said molybdenumcylinders are positioned on the corrugations adjacent to the edges ofthe sheets.
 5. A carrier according to claim 2 whereIn the carrier has atleast three sheets of corrugated molybdenum for carrying the pellets forthe dewaxing operation.
 6. A carrier for uranium oxide pellets accordingto claim 2 in which the distance between the corrugations in themolybdenum sheets is adapted to be from about 1 to about 2 times thediameter of the pellets.
 7. A carrier for uranium oxide pellets suitablefor use in the sintering of said pellets which comprises: a. a metallicsupport resistant to corrosive action under the temperature and ambientconditions of the sintering operation; b. a first corrugated molybdenumsheet positioned on said support and removable therefrom, said sheethaving substantially parallel corrugations with depressions for holdinga plurality of cylindrical uranium pellets prepared for subjection tothe sintering operation; and c. at least one additional corrugatedmolybdenum sheet having substantially parallel corrugations of the samedimensions as those of said first sheet for holding additional uraniumpellets, each of said additional sheets being positioned above andremovable from a lower molybdenum sheet separated therefrom by thepellets placed therebetween.
 8. A carrier according to claim 7 whereinthe metallic support is made of stainless steel or molybdenum.
 9. Acarrier according to claim 7 wherein the carrier has at least fivesheets of corrugated molybdenum for carrying the pellets for thesintering operation, and at least one corrugated molybdenum sheet whichdoes not carry pellets and which is spaced above the top sheet thatcarries pellets to form a heat shield and produce an even heatdistribution within the mass of pellets.
 10. A carrier for uranium oxidepellets according to claim 7 in which the distance between thecorrugations in the molybdenum sheets is adapted to be from about 1 toabout 2 times the diameter of the pellets.